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The Black Hole Information Paradox Comes to an End
- akvadrako 6y agoThe title is incorrectly copied. The original says "Nears Its End"
- mcaruso 6y agoThe title probably changed. The URL slug still has "comes-to-an-end".
- AstralStorm 6y agoSo if enough matter feel into a black hole, we'd get an entangled parallel universe? Big question then it's what is the entanglement "key" and its properties. Or how to even brute force it.
- FooBarBizBazz 6y agoBlind leading blind: My impression was that parallel universes do not feature. Rather, it was that, contrary to appearances, Hawking radiation contains all the same information that went into the black hole. However, this information appears only in the joint distribution over those photons rather than in any of the marginal distributions. Broken metaphor: You throw a coin into a black hole. Was it heads or tails? Two photons escape the black hole, both spin-up* with 50% probability -- they each appear to carry no information about the coin. But suppose that if they are the /same/ spin, then the coin was heads, and if they are /different/ spin then the coin was tails. In this way the coin's information is not destroyed, but is also not carried by any individual photon. * I have no idea if spin is actually the property of the radiation that carries the information. I also get the impression that it is later photons that must somehow be entangled with earlier ones. That -- referring to that V-shaped curve -- the black hole is storing up information about what went in up to about the halfway point in time, which it later radiates away during the second half. Waiting for an actual physisict to chime in, as, disclaimer, I don't actually know anything about this.
- bryanrasmussen 6y ago>You throw a coin into a black hole. Was it heads or tails? being heads or tails is a property of landing with all of one side of the coin facing down. This does not seem possible in the situation described.
- sudosysgen 6y agoOf course, but it doesn't matter. Any bit of information can do the trick here.
- minitoar 6y agoI read it as "every photon emitted carries information about everything that fell into the hole up until that point, but you don't get complete information about everything until the very last photon is emitted".
- andreareina 6y agoThere's a Royal Institute video featuring Sean Carroll and Jen Ouelette[1] that more fully explains the problem, but as I understand it it comes down to a quantum mechanical principle called monogamy of entanglement---there's only so much entanglement to go around, and if two particles (e.g. the pair of Hawking radiation particles) are fully entangled then they cannot have any amount of entanglement with anything else (e.g. information about the black hole). The result in TFA breaks the entanglement between the Hawking pair, allowing the outgoing particles to encode the black hole's information. [1] https://www.youtube.com/watch?v=_8bhtEgB8Mo https://www.youtube.com/watch?v=_8bhtEgB8Mo
- emerged 6y agoIt would make more sense to me if black holes had no internals, so the matter exists on the surface of the horizon. No infinities, and the matter can slowly escape over time. Maybe something in the nature of gravity which prevents more than a certain density to exist in any place and time.
- simonh 6y agoIn my mental model the internal structure of the black hole, composed of all the material that fell into it, is always preserved from some frame of reference. As you fall into a black hole the event horizon shrinks away below you and from your own POV you never cross it. Thats true of every particle or photon it traps. Of course they get twisted and distorted by the extreme gravitational forces, but in principle there is always structure. I suppose from the internal perspective, Hawking Radiation manifests as a rain of negative energy. I'm sure I'm wildly off the mark, but it's the best I can do.
- macspoofing 6y ago>As you fall into a black hole the event horizon shrinks away below you and from your own POV you never cross it. You have it backwards. From the POV of an external observer you never cross the event horizon, because that's a function time dilation, and light that you emit being more and more red-shifted as you get closer to the event horizon. From the falling observer POV, nothing really changes - or rather, what happens close to the event horizon or just past the event horizon depends on what the theory of quantum gravity says.
- simonh 6y agoI didn't address the POV of an external observer but I'm sure you're right. But what you describe for the POV of someone falling in seems consistent with what I suggested. I don't understand what you think is backwards about it.
- macspoofing 6y ago
- AtlasBarfed 6y ago"Muted at first, these effects come to dominate when the black hole gets to be extremely old. The hole transforms from a hermit kingdom to a vigorously open system. Not only does information spill out, anything new that falls in is regurgitated almost immediately."
- rapnie 6y ago> extremely old Completely OT, but this gives an indication of 'old' in this context: https://m.youtube.com/watch?v=uD4izuDMUQA https://m.youtube.com/watch?v=uD4izuDMUQA
- tines 6y ago> Information, they now say with confidence, does escape a black hole. If you jump into one, you will not be gone for good. Particle by particle, the information needed to reconstitute your body will reemerge. Most physicists have long assumed it would; that was the upshot of string theory, their leading candidate for a unified theory of nature. Does this mean string theory produced a prediction? I thought it had no predictive power and that's why people didn't like it.
- macspoofing 6y agoMaybe not. From the article: "But the new calculations, though inspired by string theory, stand on their own, with nary a string in sight. Information gets out through the workings of gravity itself — just ordinary gravity with a single layer of quantum effects...Over the past two years, physicists have shown that the entanglement entropy of black holes really does follow the Page curve, indicating that information gets out. They did the analysis in stages. First, they showed how it would work using insights from string theory. Then, in papers published last fall, researchers cut the tether to string theory altogether." Sounds like there is no dependency on string theory.
- tines 6y agoI took that to mean that they don't use string theory to prove anything per se. But it sounds like they got "insights" from string theory, which seems like it was useful for once? IANAP.
- ojnabieoot 6y agoI am a mathematician with some physics background and have been skimming this article: they took mathematical inspiration from string theory in terms of how they formulated the path integrals, but the physical concept of a string doesn’t actually appear. So string theory provided analytic tools but didn’t actually provide physics.
- andrewflnr 6y agoNot in a useful sense, it just matched with another theory. The problem with string theory remains that we can't actually measure any of its predictions.
- MichaelZuo 6y ago"Trick though it is, it has real physics in it. The gravitational path integral doesn’t distinguish replicas from a real black hole. It takes them literally. This activates some of the latent topologies that the gravitational path integral includes. The result is a new saddle point containing multiple black holes linked by space-time wormholes. It competes for influence with the regular geometry of a single black hole surrounded by a mist of Hawking radiation." Ah yes, the complex of wormhole interlinked blackholes surrounded by mists of Hawking radiation... This style of writing, without the actual math, seems to more so obscure true understanding than reveal it for such a complex construct as english words are very likely insufficient for actually capturing the true meaning. Adding the (partial?) equations of the path integral and/or the matrices would allow for an actual understanding without the confining nature of human words. In fact just thinking and writing this comment made me more confused, just a few paragraphs prior the path integral could not be fully calculated, but now here it is certain that "the gravitational path integral doesn’t distinguish replicas from a real black hole". Just how powerful is this 'mathematical trick'?
- deeeeplearning 6y ago>Adding the (partial?) equations of the path integral and/or the matrices would allow for an actual understanding without the confining nature of human words. Go read the paper if you want that. Quanta isn't a journal its a popular science mag.
- MichaelZuo 6y ago"But in terms of making sense of black holes, this is at most the end of the beginning. Theorists still haven’t mapped the step-by-step process whereby information gets out. “We now can compute the Page curve, and I don’t know why,” said Raphael Bousso at Berkeley." So it does not seem that the physicists fully understand their calculation results either. Edit: here's the arxiv link: https://arxiv.org/abs/1911.11977 https://arxiv.org/abs/1911.11977
- pdonis 6y agoThanks for the link. I find it very frustrating when pop science magazines refuse to link to the actual paper. I don't want to read their attempt to put what the paper says into layman's language; their attempts are usually way off. I want to read the actual paper. Edit: I was finally able to find links to actual papers in the article: https://arxiv.org/abs/1810.02055 https://arxiv.org/abs/1810.02055 https://arxiv.org/abs/1905.08255 https://arxiv.org/abs/1905.08255 https://arxiv.org/abs/1905.08762 https://arxiv.org/abs/1905.08762 https://arxiv.org/abs/1908.10996 https://arxiv.org/abs/1908.10996 https://arxiv.org/abs/2002.08950 https://arxiv.org/abs/2002.08950 https://arxiv.org/abs/2004.05863 https://arxiv.org/abs/2004.05863 These appear to be the papers giving the various calculations the article discusses. There are also links to some previous work that was built on: https://arxiv.org/abs/0804.0055 https://arxiv.org/abs/0804.0055 https://arxiv.org/pdf/1304.4926 https://arxiv.org/pdf/1304.4926 https://arxiv.org/abs/1408.3203 https://arxiv.org/abs/1408.3203
- goldenkey 6y agoAt least to me, it's pretty obvious that the shadow follows the form. Gravity is like an echo for mass. It seems that we are now realizing it was wrong to assume that the echo was homogenous. The electron movement process in atoms is emitting gravitational waves. The movement of any type of energy causes gravitational waves. Gravity won't be homogenous if the pattern of mass-energy emitting it, isn't homogenous. We know most mass comes from cyclic processes, ie. the inner processes of hadrons. So it stands to reason that those processes should have a unique and animated gravitational field.
- batsigner 6y agoone hydrogen atom doesn't have enough mass to produce a graviton.
- goldenkey 6y agoGeneral Relativity has no quantization, so all minor changes are infinitely perturbated. Now if you choose to go with some kind of quantum gravity, the energy of a graviton wouldn't be fixed, it would vary depending on the frequency of it. https://en.wikipedia.org/wiki/Graviton#Energy_and_wavelength https://en.wikipedia.org/wiki/Graviton#Energy_and_wavelength
- AmericanChopper 6y agoI’m glad Quanta changed the title (it should be changed here too). The research is interesting, but the paradox is in the same place it’s been in for years, ie “locality probably doesn’t survive the paradox”.
- paulpauper 6y agoIt seems like every few weeks there are these huge, complicated and profound discoveries in physics. I feel like i missed the boat on this, as if I chose the wrong profession or am missing out on something. I should have pursued math further but I probably would not have been smart enough anyway. Wikipedia has no mention of the page curve, so this is pretty cutting-edge and theoretical even by the standards of theoretical physics.
- deleted 6y ago[deleted]
- titanomachy 6y agoIf it makes you feel better, I studied physics (although only at the undergraduate level) and I still can’t really follow articles like this. If you really want to understand this stuff you basically have to dedicate your life to it, genius or not.
- v77 6y agoSean Carrol's Mindscape podcast does a pretty good job explaining things to where an average Hacker News reader would understand things. Highest recommendation. He had someone on recently talking about this paradox, the CFT-ADST correspondance and holographic theory and it was reasonably understandable.
- titanomachy 6y agoThanks for the recommendation. We used his textbook in my relativity class and he's definitely a good teacher.
- platz 6y agoDiscussed on Sean Carroll's podcast, Mindscape: https://www.preposterousuniverse.com/podcast/2020/09/21/115-netta-engelhardt-on-black-hole-information-wormholes-and-quantum-gravity/ https://www.preposterousuniverse.com/podcast/2020/09/21/115-... He seems a little non-committal if not skeptical. One telling exchange near the end regarding the gravitational path integral they used: * * * "1:18:41 SC: And there is this trick that you can introduce, ’cause what you’re supposed to do is say, well, integrate up all of the spacetimes that match on to this particular wave function you’re looking at. But the trick is, instead of integrating all the four-dimensional spacetimes that match on to this condition you’re looking at, you can just say, well, I’m going to integrate over all four dimensional spaces, so I’m going to forget about spacetime. I’m just going to do what we call the Euclidean path integral because Euclid just talked about space, not time. And… 1:19:13 NE: Oh, you went there. [laughter] 1:19:15 SC: I did, I did. This is where I’m going. And so it was sort of like you could justify… It’s a trick. It’s a mathematical trick. And it’s very rigorously justifiable in certain simple cases in quantum mechanics, and it certainly has the smell of being correct in certain more subtle cases in quantum field theory. In quantum gravity, what they were doing with it, it just seemed to be a trick so they could get a finite answer at the end of the day, and it was very unclear why it had anything to do with the real world, but they suggested it did. Maybe they were right. And since then, I think we’ve become a little more comfortable with the idea that we can use this trick of calculating quantum gravity wave functions by integrating over the Euclidean path integral, the set of all the spaces that end up looking like what we want, instead of all the spacetimes that look like what we want. 1:20:05 NE: Yes. 1:20:05 SC: And that’s what you’re doing, isn’t it? That’s the kind of wormholes that you’re invoking. 1:20:09 NE: Yes, right. That’s what I was trying to sweep under the rug. 1:20:11 SC: I know. [laughter] And you were right to do so, but I just like to live dangerously here. [chuckle] 1:20:18 SC: So Lenny and Juan have wormholes that are literally good old in spacetime wormholes, and you have wormholes that are in these fake Euclidean spaces that you used to calculate the entropy. 1:20:29 NE: That’s exactly right. Yeah, that’s exactly right. And these fake Euclidean spacetimes have more boundaries. There are more edges than our original spacetime, which means that these wormholes are connecting these… More edges than we have in our original spacetime, and therefore, it’s difficult to make sense of them in terms of the original spacetime that we’ve started with." * *
- thyrsus 6y ago"To astronauts who ask whether they can get out of a black hole, physicists can answer, “Sure!” But if the astronauts ask how to do it, the disquieting reply will be: “No clue.”" My intuition is that these astronauts would exit the black hole the way a candle exits a flame, i.e., at the atomic or subatomic level, correct?
- kazagistar 6y agoThey would exit as a stream of extremely small and infrequent particles over billions or even trillions of years, depending on the size of the black hole, in most cases ending once all the stars have died and universal expansion has emptied out almost all of the accessible universe.
- larsrc 6y agoTo which my wife says, "Well, we've always said information wants to be free." I (heart) my wife.